Intense competition for spectrum usage has arisen due to the increasingly widespread deployment of high speed networks. Measurements from the Federal Communication Commission (FCC) indicate that utilization of the licensed spectrum ranges from fifteen percent to eight-five percent. Aiming to make full use of underused spectrum resources, the IEEE 802.22 Wireless Region Area Network (WRAN) Group has proposed using spectrum between 54 megahertz (MHz) and 862 MHz in conjunction with cognitive radio techniques to efficiently exploit the existence of spectrum holes.
Use of orthogonal frequency division multiple access (OFDMA) has also been proposed in exploiting the existence of spectrum holes, since orthogonal frequency division multiple access schemes typically are agile in dynamically selecting and allocating sub channels. Cognitive radio users can use the licensed sub channels as long as the spectrum owners or primary users are absent at some particular time slot. By sensing the sub channels and dynamically selecting idle sub channels, cognitive users can flexibly exploit spectrum holes without changing the configuration and causing interference to the primary system.
Spectrum holes derived from multiple primary sub channels through use of spectrum sensing can typically be scheduled to multiple cognitive radios. Nevertheless, traditional scheduling algorithms for cognitive orthogonal frequency division multiple access systems have been designed separately from the spectrum sensing aspects necessary to more effectively exploit the ascertained spectrum holes.
Traditional scheduling algorithms for cognitive orthogonal frequency division multiple access can be summarized as: (1) schedule the user with the best channel quality among all the cognitive users for each of the idle channels; or (2) schedule the user with the best channel quality among all the sensing users. High system throughput can be achieved by scheduling users with the best channel quality among all the cognitive users for each of the idle channels, since such a scheduling scheme exploits full multiuser diversity. Under this scheme however, unfairness is introduced to sensing users as the energy for spectrum sensing is not negligible for energy constrained networks. Absolute fairness for sensing users can be satisfied in the second case but the order of the multiuser diversity in the cognitive orthogonal frequency division multiple access is generally low and throughput constrained. Accordingly, there is a tradeoff between fairness of sensing users and throughput for cognitive orthogonal frequency division multiple access systems.
The above-described deficiencies are merely intended to provide an overview of some of the problems of conventional systems and techniques, and are not intended to be exhaustive. Other problems with conventional systems and techniques, and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.